1. Field of the Invention
The present invention relates to a recording subject material that is supplied to an inkjet recording process in which liquid ink, such as water-color ink (where dye or pigment is used as coloring material) and oil ink, or solid-state ink that is a solid substance at normal temperature, and melted and made into liquid so as to be used for printing, is adopted, and, more particularly, concerns an inkjet recording sheet that is superior in ink-receiving property and image-maintaining property.
2. Description of the Related Art
In recent years, along with the rapid development of the information technological industry, various information processing systems have been developed, and recording methods and recording apparatuses suitable for these information-processing systems have been developed, and put into practical use.
Among these recording methods, an inkjet recording method has come to be widely used in offices as well as at home because of its advantages in which various recording materials can be used, and hardware (apparatuses) is comparatively inexpensive and compact, and superior in the noiseless property.
Moreover, along with recent high-resolution inkjet printers, it becomes possible to obtain high-image-quality recordings that are close to photographs, and in accordance with the development of hardware (apparatuses), various recording sheets for use in inkjet printing have been developed.
With respect to characteristics required for recording sheets used for these inkjet recording processes, in general, the following points are listed: (1) quick drying property (great ink-absorbing rate), (2) proper, uniform ink-dot diameter (without causing bleeding), (3) good graininess, (4) high roundness in dots, (5) high color density, (6) high chromaticness (without subdued color), (7) high water-resisting property, light resisting property and ozone resisting property, (8) high whiteness degree in recording sheets, (9) superior shelf life in recording sheets (without causing after-yellowing even in the case of a long-time storage, without bleeding even after a long-time storage), (10) superior dimension stability without susceptibility to deformation (less susceptible to curling) and (11) good traveling property on hardware.
Moreover, with respect to the application of photographic gloss paper used for high image-quality recordings close to photographs, in addition to the above-mentioned various properties, other characteristics, such as gloss-applying property, surface-smoothness and texture of printing paper like silver salt photographs, are also required.
In order to improve the above-mentioned various properties, in recent years, inkjet recording sheets, which have a porous structure in the coloring-material receiving layer have been developed and put into practical use. Since the inkjet recording sheets of this type have the porous structure, they are superior in the ink-receiving property (quick drying property), and have a high gloss-applying property.
For example, Japanese Patent Application Laid-Open (JP-A) Nos. 10-119423 and 10-217601 have proposed inkjet recording sheets which have fine inorganic pigment particles and a water-soluble resin and are provided with a coloring-material receiving layer having a high porosity formed on the support thereof.
These recording sheets, in particular, inkjet recording sheets having a coloring-material receiving layer with a porous structure in which silica is used as inorganic pigment fine particles, have a superior ink-absorbing property and a high ink-receiving property for forming an image with high resolution because of their inherent structure, and also exhibit a high gloss-applying property.
The above-mentioned respective inkjet recording sheets have a superior ink-absorbing property and a high ink-receiving property for forming an image with high resolution because of their inherent structure, and also exhibit a high gloss-applying property. However, from the viewpoint of gloss-applying property and texture, since these recording sheets use a support with resin coat such as polyethylene applied on both of the surfaces thereof, a high-boiling-point solvent contained in the coloring-material receiving layer is not allowed to evaporate, and this solvent is hardly absorbed in the support. For this reason, the high-boiling-point solvent remains in the coloring-material receiving layer as it is, and when, after the printing process, the recording sheets are stored under high-temperature, high moisture environment for a long time, the solvent is dispersed together with the dye in the coloring-material receiving layer, causing age-based image bleeding (hereinafter, referred to as “age-based bleeding).
Here, with respect to the inkjet recording sheet, in order to fix dye components in the ink, a compound having amino-groups and ammonium salts, in particular, a polymer compound having these, is often added thereto.
For example, many compounds have been used, and examples thereof include: a (co)polymer of diallyl ammonium salt derivative disclosed in JP-A Nos. 60-83882, 64-75281 and 59-20696; a copolymer of allyl amine salt disclosed in JP-A Nos. 61-61887, 61-72581, etc.; (meth)acrylate, (meth)acryl amid type (co)polymers having an ammonium salt, and vinyl (co)polymer such as (co)polymers of vinyl benzyl ammonium salt disclosed in JP-A Nos. 6-340163, 4-288283, 9-300810, 8-318672, 10-272830, 63-115780, etc.; modified polyvinyl alcohol (PVA) disclosed in JP-A No. 10-44588; an amine-epichlorohydrine polyadded substance disclosed in JP-A Nos. 6-234268 and 11-277888; dihalide-diamine polyadded substance disclosed in JP-A No. 10-119418; and polyamidine disclosed in JP-A Nos. 11-58934 and 11-28860. By using these compounds, it is possible to fix dyes, and consequently to prevent bleeding.
However, since any of these compounds are basically water-soluble high polymers, it is not possible to completely fix the water-soluble dyes and to sufficiently prevent bleeding, in particular, under high-temperature, high-moisture environments.
Moreover, in the case when these sheets are stored in a clear file, etc., immediately after the printing process, since moisture in the ink and high-boiling-point solvents (glycerin, diethyl glycol derivatives, etc.), slightly contained in the ink, are still allowed to remain, age-based bleeding tends to occur in this case also.
Moreover, as disclosed in JP-A Nos. 57-36692, 10-180034, 11-20302 and 8-244336, inkjet recording sheets have been known in which, an amino group and an ammonium salt are contained in the same manner as the above-mentioned compounds and a water-insoluble base latex is also contained. In the inkjet recording sheet of this type, the application of this hydrophobic latex makes it possible to improve the water resisting property.
However, in order to provide a sufficient water resisting property in the inkjet recording sheets using such latex having a hydrophobic property, a great amount of the hydrophobic latex needs to be added. The resulting problems are degradation in light resistance in images and degradation in the miscibility to pigments.
Many of these substances use a crosslinking monomer (that is, a monomer having not less than two polymerizing functional groups in a molecule) in order to form a hydrophilic monomer unit such as an amino group and ammonium salt into latex. For this reason, water-soluble ink is hardly allowed to permeate into these particles, and the ink receiving property is not sufficient. Moreover, since a particulate compound is added, this plugs voids of the porous film when applied to a receiving layer made of a porous film, resulting in degradation in the ink absorbing property. Moreover, it is not possible to prevent the generation of age-based bleeding even when these compounds are used.
Moreover, trace gases in the air such as ozone, in particular, cause age-based fading in recorded images. In particular, since the recording material having a receiving layer of a porous structure contains many voids, resistance to ozone in the air is required.
JP-A No. 2000-177235 has proposed an inkjet recording medium containing Mg ions and SCN ions in a porous layer containing an alumina hydrate. Since Mg ions and SCN ions are contained in the porous layer, this inkjet recording medium has improved light resistant and ozone resisting properties. However, the above-mentioned inkjet recording medium has a problem in which, although the above-mentioned properties are improved, it is not possible to simultaneously prevent the generation of age-based bleeding. Moreover, it has been known that in the case of the application of Ca ions instead of Mg ions, there is degradation in the ink absorbing property.
JP-A No. 7-314882 has disclosed a recording sheet having a porous ink-receiving layer containing at least one compound selected from the group consisting of dithiocarbamate, thiuram salt, thiocyanic acid esters, thiocyanates, and hindered amine compounds. With respect to specific examples of the hindered amine compounds, a compound having a structure in which all the hydrogen atoms on carbons in second and sixth positions of piperidine are substituted by methyl groups is listed, and in this recording sheet, by containing not less than one compound of the above-mentioned compound, it is possible to prevent fading in recorded images due to trace gases in the air.
However, in the above-mentioned Patent Application, no description has been given with respect to combinations of these compounds and mordants. These recording sheets have degradation in the age-based bleeding and fail to provide sufficient effects in improving endurance, in particular, in endurance for long-term use.
Moreover, JP-A Nos. 2000-255157, 2000-255158 and 2000-255160 have disclosed an inkjet recording medium containing at least one member selected from the group consisting of reducing agents having an aromatic ring. Specific examples of the reducing agents having the aromatic ring, compounds in which not less than two functional groups such as hydroxyl groups, amino groups, monoalkyl amino groups, etc., are coupled to a benzene nucleus or a naphthalene nucleus are listed. By containing these compounds, the above-mentioned recording medium makes it possible to improve image preserving property in recorded images, and consequently to prevent fading.
However, even in these recording sheets and recording media, although it is possible to provide improvements in age-based fading in the recorded images, it is not possible to sufficiently suppress the generation of age-based bleeding, and another problem is that coloring on paper surface (discoloration in white base portions), which is probably caused by these additive agents, tends to occur.
Moreover, it has been known that a sulfur-containing compound is used as an antioxidant. For example, Japanese Patent Application Publication (JP-B) Nos. 8-22608, JP-A No. 64-36479, JP-B No. 8-13570, JP-A Nos. 1-115677, 2000-177241, 2001-270220, have disclosed thioether-based compounds and mercaptobenzimidazole-based compounds that are used as sulfur-based antioxidants. However, any of the exemplified compounds are low-polarity compounds (less than 0.5 in I/O value), and the resulting problem is that it is not possible to provide sufficient effects in improving endurance even in the case of the application of these.
JP-A No. 2000-263928 has also disclosed an example in which various sulfur-based compounds are used, with high-polarity compounds (not less than 0.5 in I/O value), such as 3,6-dithiooctane-1,8-diol and thiosalicylic acid, being listed. However, in these examples, the compounds are limited to a combination of alkylene polyamine-dicyandiamide-based polycondensation substances; and the resulting problem is that these examples fail to prevent age-based bleeding.
JP-A No.7-257019 has disclosed ethylene thiourea, thiohydantoin, etc. used as a heterocyclic-ring compound, and JP-A No. 7-314883 has disclosed sulfur-containing compounds such as thiourea derivatives, thiosemicarbazide derivatives and thiocarbohydrazide derivatives. However, these examples have not disclosed anything about effects on the prevention of fading. Moreover, these examples have not described anything about combinations between these compounds and mordants.
These recording sheets fail to prevent age-based bleeding and to provide sufficient effects in improving endurance.
JP-B No.4-34953 has disclosed that the addition of a compound, such as a thiourea-based compound, a thiosemicarbazide compound and a thiocarbohydrazide-based compound, makes it possible to improve the endurance. Moreover, this has also disclosed an example in which a thiourea-based compound is combined with an organic mordant. However, there is a description that a preferable mordant to be combined therewith is quaternary ammonium salt compound, and this type of combinations fails to prevent age-based bleeding and to provide sufficient effects in improving endurance.
Furthermore, JP-A No. 2001-260519 has disclosed a recording sheet having a porous ink-receiving layer containing at least one compound of compound selected from the group consisting of a sulfinic acid compound, a thiosulfinic acid compound and a thiosulfonic acid compound. This has also disclosed that at least one compound selected from the group consisting of a thiourea compound, saccharides, a pyridine-based compound, a thioether-based compound, disulfide-based compound and a thiazine-based compound, is combined with the above-mentioned compound, and contained therein so that it is possible to greatly improve the image-preserving property. Further, these gazettes have also described that a cationic compound may be combinedly used, with polymers having primary to tertiary amino groups and quaternary ammonium salt group being exemplified. However, the compounds disclosed in Examples are only polymers having quaternary ammonium salt groups; and these cause age-based bleeding, degradation in light resisting property and ozone resisting property, thereby failing to provide sufficient effects in improving the endurance. Moreover, no description has been given with respect to the effects for improving endurance derived from the difference in kinds of these cationic polymers.
As described above, at present, an inkjet recording sheet, which has a firm colorant-receiving layer that is less susceptible to cracks, etc., is provided with a superior ink-absorbing property, a surface-smoothing property and a gloss-applying property on its recording surface, and makes it possible to form an image with high resolution, with high density, while maintaining a high ink-receiving property so that the resulting image has high light resisting property and water resisting property, and which makes it possible to store images without causing age-based bleeding even when, after the printing operation, the sheets have been stored for a long time under high temperature, high moisture environments, and has a superior ozone resisting property to prevent age-based fading in image recordings, has not been presented yet.